60
NBS Measurement Services: Dosimetry for High Dose Applications U.S. Department of Commerce National Bureau of Standards
NBS Measurement Services:
Dosimetry for
High Dose
Applications
U.S. Department of Commerce
National Bureau of Standards
Center for Radiation ResearchThe Center for Radiation Research is a major component of the National Measurement Laboratory in the NationalBureau of Standards. The Center provides the Nation with standards and measurement services for ionizingradiation and for ultraviolet, visible, and infrared radiation; coordinates and furnishes essential supportto the National Measurement Support Systemfor ionizing radiation; conducts research in radiation relatedfields to develop improved radiation measurement methodology; and generates, compiles, and criticallyevaluates data to meet major national needs. The Center consists of five Divisions and one Group.
Atomic and Plasma Radiation DivisionCarries out basic theoretical and experimental research into the • Atomic Spectroscopyspectroscopic and radiative properties of atoms and highly ionized • Atomic Radiation Dataspecies; develops well-defined atomic radiation sources as radiometric • Plasma Radiationor wavelength standards; develops new measurement techniques and
methods for spectral analysis and plasma properties; and collects,compiles, and critically evaluates spectroscopic data. The Divisionconsists of the following Groups:
Radiation Physics DivisionProvides the central national basis for the measurement of far ultra- • Far UV Physicsviolet, soft x-ray, and electron radiation; develops and disseminates • Electron Physicsradiation standards, measurement services, and data for for these radia- • Photon Physicstions; conducts theoretical and experimental research with electron,laser, ultraviolet, and soft x-ray radiation for measurement applica-tions; determines fundamental mechanisms of electron and photon inter-actions with matter; and develops advanced electron- and photon-basedmeasurement techiques. The Division consists of the following Groups:
Radiometric Physics DivisionProvides national measurement standards and support services for ultra- • Spectral Radiometryviolet, visible, and infrared radiation; provides standards dissemination • Spectrophotometryand measurement quality assurance services; conducts research in optical • Radiometric Measurement Servicesradiation, pyrometry, photometry, and quantum radiometry; and developsspectroradiometric and spectrophotometric standards and calibrationprocedures. The Division consists of the following Groups:
Radiation Source and Instrumentation DivisionDevelops, operates, and improves major NBS radiation facilities
including the electron Linac and race track microtron; develops,designs, and builds electronic and mechanical instrumentation for
radiation programs and facilities; provides national leadershipin the standardization of nuclear instrumentation; and developsnew competence in radiation sources and instrumentation. TheDivision consists of the following Groups:
• Accelerator Research• Linac Operations• Electronic Instrumentation• Mechanical Instrumentation
Ionizing Radiation Division
Provides primary national standards, measurement services, and basicdata for applications of ionizing radiation; develops new methods ofchemical and physical dosimetry; conducts theoretical and experimentalresearch on the fundamental physical and chemical interactions ofionizing radiation with matter; provides essential standards andmeasurement support services to the National Measurement SupportSystem for Ionizing Radiation; and develops and operates radiationsources needed to provide primary radiation standards, fields, andwell-characterized beams of radiation for research on radiationinteractions and for development of measurement methods. The Divisionconsists of the following Office and Groups:
• Office of Radiation Measurement• Radiation Theory• Radiation Chemistry and Chemical
Dosimetry• Neutron Measurements and Research• Neutron Dosimetry• Radioactivity• X-Ray Physics• Dosimetry
Nuclear Physics GroupEngages in forefront research in nuclear and elementary particle physics;performs highly accurate measurements and theoretical analyses whichprobe the structure of nuclear matter; and improves the quantitativeunderstanding of physical processes that underlie measurement science.
NBS MEASUREMENT SERVICES:DOSIMETRY FOR HIGH DOSEAPPLICATIONS
Jimmy C. Humphreys
Dene Hocken
William L. McLaughlin
Center for Radiation Research
National Measurement Laboratory
National Bureau of Standards
Gaithersburg, MD 20899
U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary
NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
Issued March 1988
Library of Congress Catalog Card Number: 88-600506
National Bureau of Standards Special Publication 250-1
1
Natl. Bur. Stand. (U.S.), Spec. Publ. 250-11, 49 pages (Mar. 1988)
CODEN: XNBSAV
Certain commercial equipment, instruments, or materials are identified in this paper in order to ade-
quately specify the experimental procedure. Such identification does not imply recommendation or
endorsement by the National Bureau of Standards, nor does it imply that the materials or equipment
identified are necessarily the best available for the purpose.
U.S. GOVERNMENT PRINTING OFFICEWASHINGTON: 1988
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
PREFACE
The calibration and related measurement services of the National Bureauof Standards are intended to assist the makers and users of precisionmeasuring instruments in achieving the highest possible levels of
accuracy, quality, and productivity. NBS offers over 300 differentcalibration, special test, and measurement assurance services. Theseservices allow customers to directly link their measurement systems tomeasurement systems and standards maintained by MBS. These servicesare offered to the public and private organizations alike. They aredescribed in NBS Special Publication (SP) 250, NBS Calibration ServicesUsers Guide .
The Users Guide is being supplemented by a number of specialpublications (designated as the "SP 250 Series") that provide a
detailed description of the important features of specific NBScalibration services. These documents provide a description of the:
(1) specifications for the service; (2) design philosophy and theory;
(3) NBS measurement system; (4) NBS operational procedures; (5)
assessment of measurement uncertainty including random and systematicerrors and an error budget; and (6) internal quality control proceduresused by NBS. These documents will present more detail than can be
given in an NBS calibration report, or than is generally allowed in
articles in scientific journals. In the past NBS has published suchinformation in a variety of ways. This series will help make this typeof information more readily available to the user.
This document (SP 250-11), NBS Measurement Services: Dosimetry forHigh-Dose Applications, by J. C. Humphreys, D. Hocken, and W. L.
McLaughlin, is the eleventh to be published in this new series of
special publications. It covers the dosimetry services available to
users of intense radiation fields, in particular large gamma-raysources and electron accelerators up to about 10 MeV. These are:
dosimeter irradiation services (see test numbers 49010S, 49040S, and
49041S in the SP 250 Users Guide); dosimeter calibrations (49020S and
49030S); and measurements of dosimeter characteristics (49050S).
Inquiries concerning the technical content of this document or thespecifications for these services should be directed to the authors or
one of the technical contacts cited in SP 250.
The Center for Radiation Research (CRR) is in the process of publishing
21 documents in this SP 250 series, covering all of the calibrationservices offered by CRR. A complete listing of these documents can be
found inside the back cover.
NBS would welcome suggestions on how publications such as these might
be made more useful. Suggestions are also welcome concerning the need
for new calibration services, special tests, and measurement assurance
programs
.
Joe D. Simmons Chris E. Kuyatt
Acting Chief DirectorMeasurement Services Center for Radiation Research
iii
ABSTRACT
This document describes calibration services available at the National Bureauof Standards for the standardization of high absorbed dose measurements of
ionizing radiation. The areas of application of such measurements includemedical product sterilization, electronic device radiation hardness testing anfood processing. Detailed descriptions of the NBS dosimetry procedures anduncertainty assessments are given. Measurement assurance program techniquesare discussed.
Key words: Dosimeter calibration, ionizing radiation, irradiation facilities,measurement assurance program, uncertainties.
iv
TABLE OF CONTENTS
Page
1 . Description of Service 1
2. Design Philosophy and Theory 2
3. Description of System 3
3.1 60 Co Irradiation Facilities 3
3.2 Transfer Standard Dosimeters 9
3.3 Spectrophotometer 9
3.4 Thickness Gauge 9
4. Operating Procedures 9
4.1 Internal Dosimeter Calibration 9
4.2 Irradiation of Customer Dosimeters 14
4.3 Application of Transfer Dosimeters 18
4.4 Analysis of Dosimeters 20
5. Assessment of Uncertainties 20
6. Internal Quality Control 27
7. Safety 29
References 30
Appendix A: A Report of Calibration of Irradiation of Customer's Dosimeters
Appendix B: Instructions to Customer for Irradiation of Transfer Dosimeters
Appendix C: A Report of Calibration of Results of Transfer DosmeterMeasurements
V
LIST OF TABLES
Page
Table 160 Co Decay Corrections Factors (Cd ) 13
Table 2 Various Dosimeters Types 17
Table 3 Uncertainties in Absorbed Dose Values for Irradiations withPool Source . 21
Table 4 Uncertainties in Absorbed Dose Values for Irradiations withGammacell 220 24
Table 5 Uncertainties in Absorbed Dose Values for Irradiations withVertical Beam Source 25
Table 6 Uncertainties in Absorbed Dose Values Employing TransferStandard Dosimeters 26
vi
LIST OF FIGURES
Page
Fig. 1. Photograph of model of NBS 60 Co Pool Source 4
Fig. 2. Schematic drawing of Gammacell 220 self-shielded 60 Co irradiatorin the chamber load position 6
Fig. 3. Schematic Drawing of Gammacell 220 irradiator in the irradiateposition 7
Fig. 4. Schematic drawing of teletherapy type shielded-head 60 Co
irradiator 8
Fig. 5. Examples of optical spectral scans of unirradiated radiochromicdye film dosimeter 11
Fig. 6. Typical 605nm calibration curve for radiochromic dye filmdosimeters f$. 15
Fig. 7. Typical 510nm calibration curve for radiochromic dye filmdosimeters 16
Fig. 8. Dependence of response of radiochromic dye film dosimeters ontemperature during irradiation 19
vi 1*
NATIONAL BUREAU OF STANDARDSMEASUREMENT SERVICES:
DOSIMETRY FOR HIGH-DOSE APPLICATIONS
1 . Description of Service
1.1 The National Bureau of Standards, Ionizing Radiation Division, providesdosimetry services for individual users of intense radiation fields, inparticular, large gamma-ray sources and electron accelerators up to
approximately 10 MeV. These services include the administering of knownabsorbed doses of ionizing photons to customer- supplied dosimeters (such as
solid radiochromic or liquid chemical types) or test samples that are sent to
NBS (schedule 49010S, previously 8 . 6A),
[1]* where they are packaged in
appropriate conditions of electron equilibrium and are then irradiated in the
NBS standard 6
0
Co calibration facility to specific agreed-upon absorbed dosevalues in the nominal "high-dose" ranges of 10-10 6 grays (10 3 -10 8 rads). Thedosimeters may either be spectrophotometrically read and evaluated by NBS(schedule 49040S and 49041S, previously 8 . 6D and 8.6E) or sent back to the
customer for analysis and evaluation.
1.2 Another service (schedules 49020S and 49030S, previously 8 . 6B and 8.6C)consists of supplying to customers calibrated transfer dosimeters (radiochromicdye type), packaged in appropriate equilibrium material, such as polystyrene or
aluminum, for irradiation and subsequent readout and absorbed doseinterpretation. These dosimeters are provided in sealed packages and sent to
the customer for irradiation to nominal agreed-upon absorbed dose levels in a
prescribed geometrical arrangement. The unopened packaged dosimeters are thenreturned to NBS to be read and evaluated. The absorbed dose range that is
suitable for the radiochromic dosimeters is 1 to 50 kGy (0.1 to 5 Mrad) in
water, silicon, aluminum, graphite, or certain plastics.
1.3 Finally, NBS offers special measurement services (schedule 49050S
,
previously 8.6F) such as the determination of temperature dependence, absorbeddose-rate dependence or reproducibility of dosimeter response, and measurementof detailed absorbed dose distributions in specific irradiation geometries and
in selected absorbing materials. The absorbed dose distribution measurementscan include absorbed dose profiles in heterogeneous absorbers and at surfacesand interfaces of different substances. Such information is important in
research leading to the commissioning of a radiation process, and in
measurement assurance that provides quality control of a given radiationtreatment
.
* Numbers in square brackets indicate references, to be found at the end of the
text
.
1
2 . Design Philosophy and Theory
2.1 There is a need for the standardization of high-absorbed-dose measurementsused in the radiation processing industry in order to provide measurementassurance and traceability to national standards. Some areas of applicationsof radiation processing include medical product sterilization, polymermodification, hardness testing of electronic devices, and processing of food or
food packaging materials.
2.2 The principal sources of radiation employed in processing are 60 Co gammarays and electron beams from accelerators . Other photon sources used to a muchmore limited extent are 137 Cs gamma rays and high-energy bremsstrahlung x rays.
The absorbed-dose range of interest is from about 100 Gy (10 krad) to 50 kGy (5
Mrad),depending on the application. The upper limit of electron beam energy
is assumed to be about 10 MeV to avoid the possibility of nuclear activation.The lower practical energy limit for electron beams is determined by productthickness and may be as low as 0.1 MeV for the curing of thin coatings.
2.3 The physical quantity of interest is absorbed dose in a material.Absorbed dose is defined as energy absorbed per unit mass of a specificmaterial; the units are
1 gray (Gy) = 1 joule per kilogram (J kg" 1) = 100 rad.
Generally, the materials of interest in radiation processing are made up of lowatomic -number elements such as carbon, hydrogen, oxygen, and nitrogen. Suchmaterials are quite well approximated by water. Thus, water is usually used as
the reference material in which the absorbed dose measurement is specified. Anexception is for electronic device hardness testing in which the referencematerial generally is silicon.
2.4 The primary standard employed in this service is a radiation-absorptioncalorimeter. When a material is irradiated by a photon or electron source, the
energy absorbed results in a temperature increase. The absorbed dose, D, in
the material is given by
D = E/m = cAT
where E = energy absorbed in the material,m = mass of the material,c = specific heat of the material,AT = temperature increase of the material.
The absorbed dose rate from a radiation source may be determined in a similar
manner by measuring the rate of temperature increase in an irradiated material.
For a radionuclide source, the absorbed dose rate at some other time (different
from the actual measurement time) may be calculated by using the well-known
exponential decay rate (i.e., the half life).
2
2.5 The absorbed-dose rates encountered in radiation processing can cover an
extremely wide range. For 6
0
Co sources, the rates may be as iow as a few grays
per minute; for electron beams, rates as high as 10 10 grays per second are not
uncommon. Therefore, practical routine dosimeters must either be calibrated at
approximately the same absorbed-dose rate employed in processing or theirresponse must be known to be essentially absorbed dose-rate independent.
2.6 The principal dosimetry need in radiation processing is the provision for
calibration of the response of routine dosimeters (i.e., a physical change such
as optical absorbance) as a function of absorbed dose in water over the energyand absorbed dose-rate range of interest. However, if for the specificradiation type (i.e., photons or electron beams), the energy and absorbed dose
rate requirements cannot be met by the calibration facility, then the responseof the routine dosimeters must be shown to be independent of those qualitiesover the range of interest.
2.7 An important requirement for performing proper calibration measurements is
that "electron equilibrium" conditions should exist during irradiation [2].
Such conditions exist when the number and energy of secondary electrons(generated by the primary photons) entering the volume of interest are equal to
the number and energy of secondary electrons leaving the volume. Electronequilibrium may be established by surrounding the dosimeter with an appropriatethickness of material. For example, 5 mm of polystyrene is commonly used for60 Co irradiations and the absorbed dose in polystyrene is usually converted to
absorbed dose in water. If the absorbed dose is to be specified in silicon,then an appropriate material thickness for surrounding the dosimeter would be2.2 mm of aluminum.
3 . Description of System
3.1 6
0
Co irradiation facilities . NBS employs three 60 Co gamma-ray irradiatorsfor its high-dose calibration service.
3.1.1 The pool-type source consists of a stationary annular array of twelvesource rods of about 5 kiloCurie (kCi) total activity. It is situated at the
bottom of a twelve-foot deep tank filled with water for shielding and personnelprotection. The source array is shown in Figure 1. Irradiation of dosimetersis done manually by inserting into the source array a watertight stainless
-
steel can with an inside diameter of 8 cm. The volume of uniform absorbed dose
rate is about 4 cm in diameter by 4 cm high, centered at 6.5 cm above the
inside bottom of the can on the central axis. The absorbed dose rate of this
source has been previously determined by an adiabatic graphite sphericalcalorimeter and a graphite ionization chamber of identical dimensions to an
overall uncertainty estimated to be about +0.4% at a 99% confidence level [3].
Periodic verification checks of the absorbed dose rate is done annually bymeans of reference transfer dosimeters in collaboration with the NationalPhysical Laboratory (NPL) of the U.K. The absorbed dose rate in water in May
1986 was 0.076 kGymin" 1. A complete discussion is given in reference [3] of
the sources of the uncertainties in the absorbed dose rate of this 60 Co
facility. The effect of these uncertainties on absorbed dose values assigned
to irradiations performed in this facility is discussed in Section 5.
3
4
3.1.2 The Gammacell 220 irradiator, illustrated in Figures 2 and 3 is a
commercially supplied unit (manufactured by AECL of Canada), with 24 50 Co
source rods of about 20 kCi total activity in a stationary annular array. The
source rods are located inside a massive lead-steel shielding structure that
provides personnel protection. A motorized "drawer" assembly, consisting of an
open irradiation chamber and shielding plugs above and below, can be moved up
and down through the cylindrical source array. Dosimeters are placed in the
irradiation chamber (with the drawer up) , then the drawer is lowered so that
the chamber is positioned reproducibly in the geometrical center of the sourcearray. Control of the drawer is by means of a preset timer so thatirradiations may be performed automatically. The irradiation chamber hasinside dimensions of 15 cm diameter by 20 cm high. The absorbed-dose rate in
water in May 1986 was 0.21 kGymin" 1. This rate was calibrated by means of
potassium dichromate reference transfer dosimeters from NPL in the U.K. andverified by NBS radiochromic dye film transfer dosimeters on an annual basis.The estimated overall uncertainty in this rate is about ±3% at a 95% confidencelevel [4, 5]. Discussion of uncertainties associated with absorbed dose valuesfor dosimeters irradiated with this unit is given in Section 5.
Significant radiation heating of dosimeters can occur during irradiation in
this unit, so an active cooling system consisting of a flow of chilled drycompressed air is provided to maintain the sample temperature at 24°C.
3.1.3 The vertical-beam 60 Co source consists of a single capsule containingabout 4 kCi, housed in a shielding head with a shutter and collimator assembly,as shown in Figure 4. The dosimeters to be irradiated are placed at a measureddistance from the source, the shutter assembly is opened, and the gamma raysemerge through the collimator unit into the shielded room. The irradiationtime is controlled by an automatic preset timer on the shutter assembly.
The absorbed dose rate available from this unit varies as the inverse square of
the distance from the source. At a distance of 1.5 meters, for May 1986, the
absorbed dose rate in water was 0.17 Gymin" 1. This absorbed dose rate has
been determined with an NBS standard graphite ionization chamber and is
rechecked on an annual basis. The estimated overall uncertainty in this rateis about ±1.3% at a 95% confidence level. See Section 5 for detaileddiscussion of uncertainties in absorbed dose values for dosimeters irradiatedwith this unit.
5
FRONT VIEW SHOWING DRAWER UP
Figure 2 - Schematic drawing of Gammacell 220 self-shielded Co
irradiator in the chamber load position
6
REMOVABLE E»E BOLTfOn LIFTING UNIT
Timer RANGESELECTOR SWITCHES
0R*wER 'uP~ push 3UTTQNORAwER "DOWN PUSH BUTTON
KEY SWITCH
CROSS ARM SUPPORTS
cavity ron lit t*ucxt'hiGH X 32'wiOC
FRONT VIEW SHOWING DRAWER DOWN
Figure 3 - Schematic Drawing of Gammacell 220 irradiator in the
irradiate position
7
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3 . 2 Transfer Standard Dosimeters
These dosimeters are radiochromic dye films, purchased in large batches from
Far West Technology, that have been carefully and thoroughly characterized by
NBS as to their response reproducibility, stability, absorbed dose-ratedependence, temperature and humidity dependence, and thickness. The dosimetersare type FWT-60-00, consisting of a nylon matrix incorporating an organic dye
( leucocyanide of hexa-hydroxyethyl pararosaniline) in the form of a thin solidfilm, 1.0 cm square and 50 /im thick [6]. A new batch is calibrated beforebeing utilized as transfer dosimeters as described in the Operating Procedures .
3 . 3 Spectrophotometer
The primary instrument employed for the analysis (reading) of the radiochromictransfer dosimeters is a high-performance UV/VIS spectrophotometer. Theinstrument presently used is a Varian/Cary 219. This instrument has very low
stray light characteristics so as to permit it to measure optical absorbancevalues of 3 or less with an uncertainty of less than 1%. The absorbance scaleof the instrument is checked annually with a set of neutral density filters(SRM 930D) . The wavelength scale is checked annually by means of emissionlines of well known wavelength from a mercury discharge lamp. The wavelengthscale must be within 0.2 ran of the specified value for the entire wavelengthrange (200 to 800 ran)
.
3 . 4 Thickness Gauge
The radiochromic transfer dosimeters are normally 50 fj,m thick and are measuredwith a thickness gauge to a resolution of 0 . 1 /im. The gauge is a Mitutoyoelectronic Model DGS-E with a linear displacement transducer that has a specialNBS developed digital display (not provided by the manufacturer) . Thecalibration of the thickness scales is performed annually by use of a set of
Brown & Sharpe (Super-A Jo Blocks) metric gauge blocks.
4 . Operating Procedures
4 . 1 Internal Dosimeter Calibration
The radiochromic dye film dosimeters described under 3.2 are calibrated byusing the following procedures.
4.1.1 Upon receiving a new batch of dosimeters from the manufacturer, initial
visual inspection is performed to detect any obvious flaws (fingerprints, water
marks, etc.) that might make the batch unsuitable.
4.1.2 These dosimeters are sensitive to ultraviolet (UV) light and thus must
be protected at all times from sunlight (even through windows) , fluorescent
lamps, or other sources. One effective method to achieve this is to filter
laboratory fluorescent lamps with wrap-around filters made of a special UV-
absorbing Mylar (trade named Llumar) . Even with such filters, the dosimeters
are only exposed to light during essential handling procedures, otherwise they
are stored in the dark.
9
4.1.3 Random dosimeter samples are taken from the batch to be calibrated.These samples are irradiated to specific absorbed dose levels and theirresponses are assumed to be indicative of the expected responses of theunirradiated dosimeters in the rest of that batch. The validity of thisassumption has been verified experimentally for periods of 6 to 12 months.After 12 months a new calibration of the batch should be performed.
4.1.4 Handling of the individual dosimeters is done only with fine- tippedtweezers, touching only the outer 2 mm from the edges of the 1 cm square films,and, thus, avoiding scratches, fingerprints, etc., in the center where the
analyzing light beam passes through. Small amounts of dust may be removed bygently wiping with lens tissue; however, any films that show obvious flaws suchas fingerprints, dirt, optical imperfections, etc., are discarded.
4.1.5 The films are marked in a corner with a permanent ink pen so thatconsistent orientation may be maintained in all subsequent analysis procedures.The film is placed in a special black-anodized aluminum holder that masks theanalyzing spectrophotometer light beam to a 6-mm square while holding the filmperpendicular to the sample light beam in a reproducible position. A matchingempty holder is placed in the reference light beam. With no films in eitherholder, the spectrophotometer may be properly balanced.
4.1.6 All films are irradiated to a low absorbed dose level of 1.0 kGy beforeany optical analysis is performed. The slight coloration developed in thefilms as a result of this uniform low absorbed dose is proportional to the dyeconcentration in the films. Thus, optical absorbance readings of the filmsafter this initial "pre-calibration" irradiation are made in order to eliminatethe effects of variations in dye concentration and, therefore improve theprecision of the response of the system. These "pre-calibration" irradiationsare performed with the films packaged ten at a time under equilibriumconditions as described in 4.1.8.
4.1.7 Initially, each film is analyzed by a wavelength scan of thespectrophotometer from 5 ran above the primary absorption peak (at 605 ran) to 5
ran below on an expanded absorbance scale (0.1A full scale, where A representsoptical absorbance units) . This scan will sometimes show optical interferencefringes in the form of oscillations (see Fig. 5) . If the peak-to-peakoscillations are greater than some specified value (0.001A), then the resultsare considered to be unsatisfactory. The holder and film are removed from the
spectrophotometer and the film is rotated 90° and then read again. If the
oscillations are less than the specified value, then the film is consideredacceptable. If all possible orientations are tried and the oscillations are
still greater than the specified limit, then that film is rejected and another
is selected to be tested in the same fashion. If the film reading is
acceptable, then it is marked with permanent ink in the lower left corner with
a unique code number. These initial readings are designated Ax
. All
subsequent readings of the film are done with this orientation. The
wavelengths of analysis are 605 ran and 510 ran, using a Varian/Cary 219
spectrophotometer with a spectral bandwidth of 3.5 ran.
10
- 1-M-|-r • —
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~<- . 4_|
illi . : .
v- j—f--—
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FIGURE 5 Examples of FWT A Q scans, from 610 nm down to 600 nm
,
showing various oscillations, for different orientations.
NOTE: Spectrophotometer settings:
RANGE: 0.1 ABS ; S.B.W.: 3.5 nm ; PERIOD (sec):1.0; CHART DISPLAY: 5 nm/cm; SCAN RATE: 0.2 nm/sec.
A. First position: oscillations are too large and are notacceptable; film rotated 90°.
B. First rotation f second position): oscillations are verysmall and can be ignored; this is the most acceptable readingof all
.
C. Second rotation (third position): oscillations, as in A, arenot acceptable.
D. Third rotation (fourth position): oscillations are withinspecification; however, taking an average between the highestand lowest readings around 606 nm would be required for anaccurate reading of low absorbance values of this film forthis orientation.
11
4.1.8 Before the calibration irradiations, the dosimeter films are stored at
room temperature (~ 24°C) in a controlled humidity environment (within the
range of 40 to 50% R.H.) for at least 24 hours [7]. After this period, thedosimeters are packaged in appropriate equilibrium build-up material. For theabsorbed dose to be specified in water (or tissue) , the equilibrium materialused is polystyrene; for absorbed dose in silicon, the equilibrium materialused is aluminum. The equilibrium material is in the form of 25-mm squareblocks, which are 5 mm thick for polystyrene and 2.2 mm thick for aluminum.There is a 12-mm square cavity, 1 mm deep, in one block of each pair of blocks.A group of five dosimeters is stacked and placed in the cavity between the two
blocks of the appropriate material then heat sealed in two pouches of lOO^um
thick polyethylene; an inner black layer for light protection, then an outerclear layer. After packaging, the dosimeters are ready for irradiation.
4.1.9 Most calibration irradiations are performed in the NBS 60 Co pool source.
Each dosimeter package is placed in a polystyrene foam holder fitted into the
stainless steel can so as to locate it at the geometrical center of the sourcearray. Irradiations are done by manually lowering the water-tight irradiationcan (attached to a long handling pole) into the source array, noting the clocktime, then removing the can (manually) at the end of the calculated Irradiationtime. The irradiation times for given absorbed doses are calculated beforeirradiations are started, based on previous verifications of the sourceabsorbed dose rate and corrected for the exponential radioactive decay for 60 Co
(based on a half-life of 5.27 years). Decay corrections are done every two
days to provide a current absorbed dose rate. The decay correction factor is
given by the equation:
Dp
= DQ e" At
where Dp
= absorbed dose rate on the desired date,
DQ= absorbed dose rate on December 31 of the previous year,
A = 6
0
Co decay constant, andt = number of days from December 31 of the previous year to the desired
date
.
Now,
A=0.693147
Tv (years) • 365.25 days/year
where T%
= half life for 60 Co = 5.2714 years.
Thus A = 3.60006 x 10^/day.
The decay correction factor = Cd = e_At . Values for C d for various elapsed
times are given in Table 1
.
To use Table 1, determine the number of days since the previous December 31
(for which the absorbed dose rate was stated). Then multiply the correction
factors from Table 1 that correspond to the total number of elapsed days. For
example, if the absorbed dose rate on April 23 was desired, the number of
elapsed days (for a non-leap year) would be 113 days. To determine the decay
correction factor, look up the factor where the horizontal row for "100"
12
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13
intersects the vertical "10" column corresponding to 110 days. This factor is
0.9611. The factor for "3", the remaining number of days, in the first row is
0.9989. Multiply these two factors to give the correction for 113 days:
0.9600. Multiply this factor by the absorbed dose rate for the previousDecember 31 to give the dose rate for April 23.
4.1.10 A typical calibration of a new batch would cover an absorbed-dose range
of 1 kGy to 50 kGy with absorbed dose values of 2, 5, 10, 15, 20, 30, 40 and
50 kGy.
4^1.11 After irradiation, the dosimeters are stored for approximately 24 hoursto allow for complete development of the dye [7]. After this period, the finalspectrophotometer readings (designated A2 ) are made, taking care that the same
orientation of each film is used as for the initial Ax
readings.
4.1.12 Finally, the thickness of each dosimeter is read at three points acrossthe film corresponding to where the spectrophotometer light beam passes throughthe dosimeter film. The mean value of these measurements is used as the filmthickness
.
4.1.13 All values of initial absorbance, Ax , final absorbance after
irradiation, A2 , and thickness in mm, t, for each dosimeter are recorded in a
data book. The response of the dosimeter is given by, R2
4.1.14 The mean R2for each group of five dosimeters irradiated together is
plotted against the absorbed dose in the specified material. A curve is fittedthrough the data by means of a least squares regression method such as a
polynomial fit. In general, the curve will be nonlinear, at least over certainportions of the absorbed dose range. Data for both wavelengths of analysis,605 nm and 510 nm, are used to generate separate calibration curves. SeeFigs. 6 and 7 for examples.
4.1.15 Dosimeters from the calibrated batch irradiated to some unknownabsorbed dose are read according to the procedures of this section and the
resulting absorbed dose is obtained from the calibration curves. The 605 nmcalibration curve is used primarily to determine the absorbed dose value; the
510 nm results are used generally for redundancy to check on possible erroneous
interpretation of the 605 nm results.
4 . 2 Irradiation of Customer Dosimeters
4.2.1 Various types of dosimeters may be submitted by customers for
irradiation to various absorbed dose levels. Table 2 gives a brief listing of
some typical dosimeter types and the applicable absorbed dose range for which
they may be utilized; other types may also be processed.
4.2.2 The irradiation geometry used for these dosimeters depends on their size
and shape. In general, if the requested absorbed dose is in water, then a
container made of polystyrene with a 5-mm wall thickness is used to hold the
dosimeters in the proper location (i.e., the center of the source array for the
14
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Table 2
VARIOUS DOSIMETER TYPES
Dosimeter Type Absorbed Dose RangekGy in H2 0
FWT-60-00 dye film3 1-50
Harwell Red Perspexb 5-50
Harwell Amber Perspexb 1-20
Harwell HX Perspex and Radixclear PMMAb 3-100
Ceric-cerous sulfate solutions 0.3-100
Potassium and silver dichromatesolutions 1-50
Fricke (ferrous sulfate) solution 0.01-0.4
Thermo luminescence dosimeters 0.01-1(LiF, CaF2 ,
etc.)
FWT Opti-chromic 0.02-10(liquid in optical waveguide)
a The material of this film is primarily "Elvamide"nylon from DuPont . The radiochromic sensor is hexa-hydroxyethylpararosaniline cyanide.
b "Perspex" and "Radix" are trade names for polymethyl methacrylate(PMMA)
.
17
pool source) during irradiation. This container may be in the form of squareblocks for FWT-60-00 thin dye films as used in the internal NBS calibration, or
in the form of a cylindrical cup for Red Perspex or similar type dosimeters.These containers supply the material needed to provide electron equilibriumconditions during irradiation as previously discussed in 2.7. The Red Perspexdosimeters, for example, are about 3-mm thick and a correction for selfattenuation (of about 3%) is necessary in order to specify the correct averageabsorbed dose rate in the dosimeters during calibration.
4.2.3 Upon completion of the irradiations requested by the customer, the
dosimeters are returned promptly to him. In the case of fragile or unstabledosimeters, it is sometimes necessary to specify special shipping conditions.For example, because of instabilities following irradiation, Red Perspexdosimeters should be sent by express overnight mail service and should beprotected from temperature extremes during that period. Aqueous chemicalliquid dosimeter ampoules also require such precautions, as well as protectionagainst breakage by careful packaging. After double checking the irradiationtimes and calculations of the absorbed-dose rates for that day, a Report ofCalibration is prepared and sent to the customer specifying the absorbed dosesgiven to his dosimeters (see Appendix A) . The customer then formulates his owncalibration curve based on the NBS absorbed-dose values and readout of thedosimeters with his own instrumentation.
4 . 3 Application of Transfer Dosimeters
4.3.1 When a customer requests dosimeters to be supplied for irradiation inhis facility, the procedures of 4.1.4 to 4.1.8 are followed, using unirradiateddosimeters from a calibrated batch, i.e., reading initial absorbances
,humidity
conditioning, and then packaging the dosimeters.
4.3.2 The requested number of packaged unirradiated dosimeters (plus somecontrols) are sent to the customer, along with instructions on proper handling(e.g., do not open the packages), the proper absorbed dose level to be given (1
to 50 kGy) , as well as reporting any special environmental conditions (e.g.,elevated temperature during irradiation) (see Appendix B) . If the temperatureof the dosimeter package is expected to exceed 30°C during irradiation in thecustomer's facility, then the customer is requested to measure that temperatureduring the irradiation and provide NBS with those data (preferably as a
function of time) in order that NBS can apply the proper correction factors to
the dosimeter response (see Fig. 8).
4.3.3 When the irradiations are completed by the customer, he sends the
dosimeter packages back to NBS. The packages are opened at NBS and the
dosimeters read as soon as possible following the procedures of 4.1.11 to
4.1.15. The results are corrected for elevated irradiation temperature, if
required, and the results are compared to the nominal absorbed dose the
customer reportedly gave the packages. Results are then supplied to the
customer in the form of a Report of Calibration (see Appendix C for anExample)
.
4 . 4 Analysis of Dosimeters
4.4.1 Reading of customers' dosimeters is done in a manner similar to thatused for the internal calibration procedures detailed in 4.1. For FWT-60-00
18
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19
dye film dosimeters, the procedures are identical to those discussed in 4.1.
For other types of dosimeters, the spectrophotometric analysis is tailored to
meet their particular requirements. For example, Red Perspex dosimeters are
read at only one wavelength (640 ran) and require a different holder than the
FWT-type film.
5 . Assessment of Uncertainties
5.1 The estimates of uncertainties for the absorbed dose values assigned to a
given group of dosimeters irradiated together in the 60 Co pool source are givenin Table 3. The designation of the types of uncertainties (A and B) followsthe recommendations of the BIPM Working Group on the Statement of Uncertainties
[8, 9] . Type A is the random component and is stated as an estimate of a
sample standard deviation. These can be determined by standard (objective)statistical methods. Type B uncertainties are determined by "other methods",thus implying some element of subjective evaluation. Type B uncertainties may,
in some cases, correspond roughly to "systematic" contributions, but this maynot always be true. In line with the BIPM recommendations, the term"systematic" is avoided. Those recommendations also treat both types ofuncertainties equally; that is, as being equivalent to "standard deviations".Thus, each type is combined separately in quadrature (i.e., the square root ofthe sum of the squares) . An overall combined uncertainty is obtained bycombining the two types once again in quadrature. Finally, a total uncertaintyis obtained by multiplying a "safety" factor (such as 2 or 3) ; in this case thefactor chosen was 3. For a normal population distribution this factor wouldcorrespond approximately to the statistical "Student's t-factor" at a 99%confidence level and a sample size of about 14 (13 degrees of freedom),assuming that the combined uncertainties can actually be treated as a standarddeviation.
5.2 The values of the uncertainties given in Table 3 for irradiations donewith the pool source were determined from published literature or fromexperimental estimates. The published values usually are given for a 95% or
99% confidence level, so the values given in Table 3 are obtained by dividingthe published values by two or three respectively so as to correspond to a
"standard deviation" of one. The experimental estimates are usually the
"maximum" expected range which would correspond roughly to a 99% confidencelevel. Thus, values for Table 3 were obtained by dividing these estimates bythree. The values of uncertainties listed are stated in terms of percentagesof the sample mean of the mesured quantity. This corresponds to a percentageof an estimated coefficient of variation [10] given by:
100 a- 100. sx
x
whereA
estimated standard deviation of the sample mean,
x mean of the sample size n,
and computed sample standard deviation
20
Table 3
UNCERTAINTIES IN ABSORBED DOSE VALUES
FOR IRRADIATIONS WITH POOL SOURCE
Source of Uncertainty Type A (%) Type B (%)
( random) (other)
Graphite calorimeter/ion chamber 0.14measurement of pool source dose rate
Source decay, half life 0.01
Timing of irradiations 0.23
Conversion of dose rate: graphite to 0.30water, silicon, etc.
Attenuation corrections in equilibrium 0.03material
Effect of dosimeter positioning in 0.25irradiation can
Geometrical effects of equilibrium 1.00material on dose rate
Source decay correction for given date 0.02
Type A, Type B combined (in quadrature), 0.34 1.05
separately
Combined (in quadrature) 1.11
TOTAL: 3X Combined 3.3
Zl
The sources of the uncertainties are as follows:
(1) The calorimeter/ion chamber measurements of the pool source absorbeddose rate were analyzed in reference [3] for all possible sources of errorcontributions such as core mass, electrical power, attenuation, and heatingrate for the calorimeter, and air mass, current measurement, and collectionefficiency for the ion chamber. All factors were combined in quadrature(square root of the sum of the squares) to give an overall value of 0.43% at
a 99% confidence level. The value for Table 3 would be 0.43% divided by 3
or 0.14%.
(2) The uncertainty in the half life of 60 Co was reported to be 5 parts out
of 52,714 or 0.01% [11]. The level of confidence was not reported, so it
was assumed to correspond to one standard deviation.
(3) The uncertainty in the timing of the irradiations was estimated to be a
maximum of 5s for the manual manipulation of the irradiation can into thesource array. This would correspond roughly to a 99% confidence level, so
dividing this time by 3 would give an uncertainty of 1.7s for one standarddeviation. For a 1 kGy absorbed dose at the current absorbed dose rate, the
irradiation time is about 750s: 1.7s is about 0.23% of this time.
(4) For the conversion of the absorbed dose rate of the source from onematerial (e.g., graphite) to another (e.g., water), the uncertainty in the
ratio of mass energy absorption coefficients for photon spectra withsignificant scattered components down to about 100 keV is estimated to beabout 0.6% at a 95% confidence level [12]. Thus, the uncertainty value forone standard deviation would be 0.6% divided by 2 or 0.3%.
(5) For the correction for attenuation in the equilibrium buildup materialsurrounding the dosimeters, the uncertainty in the mass attenuationcoefficients down to 5 keV is about 2% at a 95% confidence level [12], or 1%
corresponding to one standard deviation. The correction factor is about 3%,
so the uncertainty in the factor would be about 0.03%.
(6) The effect of variation of the location of the dosimeter packageduring irradiation can be estimated from isodose profiles that weredetermined previously. With a location imprecision of about 0.5 cm, the
uncertainty is estimated to be 0.5% at a 95% confidence level. Theuncertainty value corresponding to one standard deviation would be 0.25%.
(7) The effects of different geometrical configurations for the equilibriummaterial (i.e., a cylinder compared to a slab) has been examined previously
[13] and are estimated to contribute about a 3% uncertainty at a 99%
confidence level. The uncertainty corresponding to one standard deviationwould be 1%.
(8) The uncertainty due to the calculation of the correction for sourcedecay for a particular date can be estimated from the values in Table 1
.
Corrections are made every two days, so the maximum uncertainty would be
about 0.07% (the difference between day 0 and day 2 values) at a 99%
confidence level. The uncertainty corresponding to one standard deviationwould be 0.02%.
5.3 For irradiations done with the Gammacell 220 irradiator, the estimated
uncertainties for absorbed dose values are given in Table 4. Most of the
uncertainties are the same as for the pool source irradiations shown in Table 3
with some notable exceptions:
(1) The absorbed dose rate has been measured only with the NPL dichromate
reference transfer dosimeters [4, 5]. NPL gives an overall uncertainty of
2Z
3% at a 95% confidence level for use of these dosimeters. The uncertaintycorresponding to one standard deviation would be 1.5%. Other dosimetrymethods (such as calorimetry) are being developed to improve the accuracy of
the determination of this absorbed dose rate in the future.
(2) The other uncertainty factor that is different from the pool source is
the timing of irradiations. There is a significant transit time when the
dosimeters are entering and leaving the radiation field that is notaccounted for by the irradiation timer. This transit time has beendetermined to effectively add 4.1 seconds to the irradiation time set on the
automatic timer. This transit time was determined with an estimateduncertainty of one second at a 95% confidence level, or 0.5s correspondingto one standard deviation. To minimize the effect of the transit timeuncertainty, irradiation times of at least 10 minutes are used. Thus, theuncertainty in irradiation time caused by this transit time uncertaintywould be 0.08% for a 10 minute irradiation.
5.4 For irradiations done with the vertical beam source, the uncertainties in
absorbed dose values are given in Table 5. Some of the uncertainties have the
same values as for the pool source discussed in 5.2. Those that are differentare
:
(1) Calibration of the exposure rate at a specific distance from thesource by a standard graphite cavity ionization chamber to an estimateduncertainty of ± 0.7% at a 95% confidence level [14]. Thus, the uncertaintycorresponding to one standard deviation would be 0.35%.
(2) Conversion of the exposure rate to absorbed dose rate in watercontributes an additional uncertainty of about 1.1% [15] due to factors suchas the uncertainties in the values for W (average energy required to producean ion pair in air), the displacement correction factor, the ratio of energytransfer and energy absorption coefficients, and the ratio of absorbed doseto kerma. The uncertainty value is for a 95% confidence level. The valuecorresponding to one standard deviation would be 0.55%.
(3) The uncertainty value given in Section 3.1.3 (±1.3%) is obtained bycombining the uncertainties from (1) and (2) in quadrature.(4) The accuracy of timing of irradiations is determined by the uncertaintyof the shutter transit time (~0.6s) and is estimated to be about 0.2s at a
95% confidence level. The value corresponding to one standard deviationwould be 0.1s. The minimum irradiation time that would generally be usedis about 1000s, so the uncertainty contribution would be about 0.01%.
(5) The error in positioning the dosimeters at a location different fromthat of the calibrating ion chamber was estimated to be 1.0 mm at a 95%
confidence level for a source distance of 1000 mm. The value correspondingto one standard deviation would be 0.5 mm and would contribute a randomuncertainty of about 0.05%.
5.5 The uncertainties in absorbed dose values assigned to the results when NBS
supplies transfer standard dosimeters to a customer for irradiation in the
customer's irradiation facility are given in Table 6. The transfer dosimetersare calibrated only in the pool source, so the combined uncertaintiesassociated with irradiations with that source are listed in the first line of
Table 6. Additional uncertainties (corresponding to one standard deviation)
associated with the response characteristics of the transfer dosimeters are
listed in the rest of Table 6. The total uncertainty is obtained in the same
manner as that discussed in 5.1.
23
Table 4
UNCERTAINTIES IN ABSORBED DOSE VALUES
FOR IRRADIATIONS WITH GAMMACELL 220
Type A (%) Type B (%)
Source of Uncertainty (random) (other)
NPL dichromate reference 1 . 50
dosimeter measurement of dose rate
Source decay, half life 0.01
Timing of irradiations: 0.08transit dose
Conversion of dose rate: 0.30water to silicon, etc.
Attenuation corrections in 0.03equilibrium material
Effect of dosimeter positioning 0.25in irradiation chamber
Geometrical effects of equilibrium 1.00material on dose rate
Source decay correction 0.02for given date
Type A, Type B combined (in 0.26 1.83quadrature)
,separately
Combined (in quadrature) 1.85
TOTAL: 3X Combined 5.5
Table 5
UNCERTAINTIES IN ABSORBED DOSE VALUES
FOR IRRADIATIONS WITH VERTICAL BEAM SOURCE
Source of Uncertainty
Graphite ion chambermeasurement of exposure rate
Conversion of exposure rateto absorbed dose rate in water
Type A (%)
(random)Type B (%)
(other)
0.35
0.55
Source decay, half life
Timing of irradiations:shutter transit time
0.01
0.01
Conversion of dose ratewater to silicon, etc.
0.30
Attenuation corrections in
equilibrium material
Effect of dosimeter positioning:distance from source
0.05
0.03
Source decay correctionfor given date
0.02
Type A, Type B combined(in quadrature)
,separately
Combined (in quadrature)
TOTAL: 3X combined
0.05
0.72
2.2
0.72
25
Table 6
UNCERTAINTIES IN ABSORBED DOSE VALUES
EMPLOYING TRANSFER STANDARD DOSIMETERS
Source of Uncertainty Type A (%) Type B (%)
(random') (other)
Combined (in quadrature) fromTable 3 0.34 1.05
Transfer standard dosimeterresponse 1 . 00
Dosimeter response temperaturecorrection 0.50
Time dependence of dosimeterresponse 0.50
Effects due to differences in photonenergy spectra of sources 0.50
Type A, Type B combined (in quadrature),separately 1.06 1.36
Combined (in quadrature) 1.72
Total: 3X Combined 5.2
26
6. Internal Quality Control
6.1 Measurement assurance program (MAP) type techniques are used to ensurethat calibration irradiations are performed correctly and the process is in a
state of statistical control [16].
6.2 A number, n, of check standards, in the form of calibrated radiochromicdye film dosimeters, are placed immediately adjacent to the test dosimetersduring each irradiation. After irradiation, the check standard dosimeters are
analyzed to produce a sequence of absorbed dose readings cx , . .
.
,cn .
Thus, for a given absorbed dose level, the accepted value of the check standardis the mean of those values:
The estimated total standard deviation of the check standard dosimeter responseis
The number of degrees of freedom, u,required to estimate the initial value for
the actual standard deviation can be determined by choosing how close the
estimate should be to the true value at a given confidence level. For example,if the estimate is to be within 20% of the true standard deviation at a 95%
confidence level, then the degrees of freedom, v = 46 = n-1, or n = 47measurements [see sec. 2.4 of reference 14]. As the measurement assuranceprogram progresses, additional data are obtained on the variability of theresponse of the check standard dosimeters, and a more reliable value for the
estimated standard deviation may be computed. This is done by "pooling" the
standard deviations obtained on separate occasions for the same process. If
individual standard deviations are sx
,
s
k with degrees of freedomv
x , ,
f
k ,respectively, then the pooled standard deviation is
n
i = l
n
r
SP v
x+ . . .+i/k
The degrees of freedom associated with sp
is v = ux+ . . . . +i/
k .
27
6.3 Control limits may be chosen for future check standard dosimeterobservations (where each observation is the mean of n = 5 readings) using the
following:
Upper control limit = Ac
+ —
—
7n
3sc
7nLower control limit = A
c
In this case, a safety factor of 3 was chosen; a factor of 2 is sometimes used,or for a near-normal response distribution, the appropriate percent point ofthe Student's t distribution, ta , 2 (v), may be used, where 1-a is the specifiedconfidence level.
6.4 The control procedure applied to each future calibration depends on a teststatistic, T, calculated from the value of the check standard, c f (the mean ofn = 5 readings) by the following:
T =Sc
7n
If T < 3, then the process is in control. If T > 3, then the process is "outof control" and remedial action is required.
6.5 Control charts are used to determine if the calibration irradiations arebeing performed in the proper way. Initial measurements are made to determinethe mean dosimeter response and variability for each absorbed dose level. Oncethe dosimeter system response is adequately characterized, then control chartsare drawn up that provide a baseline value for each absorbed dose level andappropriate control limits as discussed in 6.3. All subsequent readings areplotted as a function of time on these charts. All the readings should fallwithin the control limits except for the few that would fall outside due to
pure chance (i.e. , about one in a hundred for a value of a = 0.01 or the 99%
confidence level) . If readings fall outside the control limits more often thanwould be expected by pure chance, then the process is "out of control" and mustbe investigated and corrected.
6.6 The radiation response of the check standard dosimeter batch may change
(drift) slowly with time. An "out of control" situation on the control chartmay indicate such a drift in response. In that case, it is necessary to
completely characterize the batch response again as was done initially in
setting up the control chart.
6.7 Quality control procedures are used in other areas such as data reduction
and report generation. All irradiation data, such as source decay corrections
and calculated irradiation times, are double -checked for accuracy. Anexperienced, highly- trained technician performs all calibration irradiations
and analysis of dosimeters. Senior scientific staff review all results and
28
check all calibration reports. The condition of each group of test dosimetersto be irradiated is evaluated when they are received to ensure they are of highquality. Any unusual condition or appearance is checked by consulting with the
requesting customer before proceeding. Checks of the performance of the
various analytical instruments used are done on a periodic basis as describedin Section 3. Plans are underway to further automate the data handling, such
as automatic timing of the irradiation calibration.
7 . Safety
7.1 Operation of these calibration services involves use of high- intensityionizing radiation sources that have the potential to expose staff personnel to
hazardous levels of radiation. NBS health physics rules and Nuclear RegulatoryCommission regulations require that personnel using these sources have formaltraining in the correct operation and safe use of them. In some cases, testsare given after the training to verify that the personnel have understood themost important aspects of that training.
7.2 Access to all high- intensity source areas is limited to those staff with a
need to use them. Doors to these areas are kept locked at all times withcontrol maintained over the minimum number of keys available to the areas.
29
References
1. Uriano, G . A. Garner, E.L. Kirby, R.K. , and Reed, W.P., Editors. NBSCalibration Services Users Guide 1986-1988 Edition. NBS Special Publication 250
and Fee Schedule for SP 250, Office of Physical Measurement Services, NationalBureau of Standards, Gaithersburg , MD 20899 (1986)
2. Greening, J. R. , Fundamentals of Radiation Dosimetry. Chapters 5 and 6,
Medical Physics Handbook 6, Adams Hilger Ltd., Bristol, U.K. (1981).
3. Petree, B. , and Lamperti, P., "A Comparison of Absorbed Dose Determinationsin Graphite by Cavity Ionization Measurements and by Calorimetry" , J . Res
.
Natl. Bur. Stds., 71C, No . 1 , pp. 19-27 (1967).
4. Sharpe,P.H.G., "Dichromate Dosemeter Reference Service", National Physical
Laboratory, U.K. (1984).
5. Sharpe, P.H.G., Barrett, J.H., and Berkley, A.M., "Acidic AqueousDichromate Solutions as Reference Dosimeters in the 10-40 kGy Range", Int. J.
Appl. Radiat. Isot., 36, pp. 647-652 (1985).
6. McLaughlin, W. L. , Jarrett, R. D., Sr., and Olejnik, T. A., "Dosimetry",Chapter 8 in Preservation of Food by Ionizing Radiation . Vol. I,
Josephson, E. S., and Peterson, M. S., Eds., CRC Press, Boca Raton, FL, pp.189-245 (1982) .
7. Levine , H.,McLaughlin, W. L. , and Miller, A., "Temperature and Humidity
Effects on the Gamma-Ray Response and Stability of Plastic and Dyed PlasticDosimeters", Radiat. Phys . Chem.
, 14, pp. 551-574 (1979).
8. Kaarls, R.,"Report of the BIPM Working Group on the Statement of
Uncertainties", 1st meeting, 21-23 Oct. 1980.
9. Giacomo, P., "News From the BIPM", Metrologia, 17, pp. 66-74 (1981).
10. Ku, H.H. , "Notes on the Use of Propagation of Error Formulas", PrecisionMeasurement and Calibration . NBS Special Publication 300-Vol.l, pp. 331-341
(1969).
11. NCRP Report No. 58, 2nd Ed., "A Handbook of Radioactivity MeasurementsProcedures", National Council on Radiation Protection and Measurements,Bethesda, MD (1985).
12. Hubbell, J.H., "Photon Mass Attenuation and Energy-absorption Coefficients
from 1 keV to 20 MeV" , Int. J. Appl. Radiat. Isot., 33, pp. 1269-1290 (1982).
30
13. McLaughlin, W.L., "A National Standardization Programme for High-DoseMeasurements", High-Dose Measurements in Industrial Radiation Processing, IAEATech. Report No. 205, IAEA, Vienna, pp. 17-32 (1981).
14. Loftus, T.P., and Weaver, J.T., "Standardization of 60 Co and 1 3
7
Cs Gamma-Ray Beams in Terms of Exposure", J. Res. Natl. Bur. Stds., 78A, No . 4 , pp. 465-
476 (1974).
15. ICRU Report 14 "Radiation Dosimetry: X Rays and Gamma Rays with MaximumPhoton Energies Between 0.6 and 50 MeV" , Int. Com. on Radiat. Units andMeasurements, Bethesda, MD (1969).
16. Belanger, B. Measurement Assurance Programs Part I: General Introduction,
and Croarkin, C. , Part II: Development and Implementation. National Bureau ofStandards Special Publication 6761 and 676II (1984).
17. Natrella, M.G., Experimental Statistics . NBS Handbook 91 (1963).
31
U.S. DEPARTMENT Of COMMERCEKATKWAl IURIAU Of STANDARD*
OAiTMiRiiURO. marviano io«M Test 536/ 111111-86NBS DB 100/100XRG- 322December 26, 1985
REPORT OF CALIBRATIONof
Far West Technology, Inc. Type 60-00 Rad1ochron1c Dosimeters
for
Kilorad Corporation89 Irradiator AvenueMoline, IL 60609
Attention: Jeffrey DoeChemistry Lab Supervisor
Ref. P.O. No.: Ill
Far West Technology radlochromlc dosimeters, type 60-00, supplied by KiloradCorporation, were irradiated, ten at each dose, under controlled conditions usinggamma radiation from a standard 60 Co source. During Irradiation the dosimeterswere held between 5.0-mm thick blocks of polystyrene, which were sealed insidepolyethylene packets. The relative humidity at the time of sealing was 56%. The
temperature during Irradiation was 24°C. The dates of Irradiation and values of
absorbed dose were as follows:
Dosimeter No. Date of Irradiation Absorbed Dose in WaterCkGy)* (Mrad)
101-110 19 Dec. 1985 10.0 1.00
111-120 20 Dec. 1985 15.0 1.50
121-130 20 Dec. 1985 20.0 2.00
131-140 19 Dec. 1985 25.0 2.50
141-150 23 Dec. 1985 30.0 3.00
*1 kGy = 0.1 Mrad
APPENDIX A
A-l
Test 536/ HHU-86NBS DB 100/100XRG-322December 26, 1985Page 2 of 2 pages
The attached page describes uncertainties and related factors In high-dosecalibrations, such as the one covered by this Report of Calibration. Any questionsregarding environmental conditions, different types of materials used, and
systematic uncertainties associated with these calibrations can be answered by thisattachment. If there are further questions, they should be directed to the firstindividual named below.
Measurements were made by
D. G. Hocken, Calibrations Technician(301)921-2201
Approved by
J. W. Moiz, LeaderX-Ray Physics Group
For the Director
A. S. Caswell, ChiefIonizing Radiation DivisionCenter for Radiation Research
APPENDIX A
A-2
UNCERTAINTIES AND RELATED FACTORS IN HIGH- DOSE CALIBRATIONS
Standard High-Dose Gamma-Ray Irradiations at NBS(Estimated uncertainty: ± 3.3% at a 99% confidence level)
The high-dose calibrations at NBS (schedule 49010S) involve the
administration of 60 Co gamma radiation absorbed doses in certain materials(e.g., water, carbon, aluminum, silicon, polystyrene, etc.), underenvironmentally controlled conditions. The dose values are based onstandard graphite calorimetry measurements, which are corrected by certainmodifying factors (the estimated photon spectrum, tabulated weighingfactors, such as radiation energy absorption and attenuation factors, andsource decay factors) . The irradiations are usually carried out using the
NBS calibrated 60 Co water-well type irradiator. The uncertainties citedabove are pertinent to absorbed values specified in a given material, withthe dosimeters irradiated under approximate equilibrium conditions, in the
absorbed dose region of 1 KGy and upward.
Absorbed Dose Evaluations Based on Traceability throughMailed Chemical Transfer Dosimeters(Estimated uncertainty: ± 5.2% at a 99% confidence level)
It must be recognized by calibration users that routinely applied chemicaldosimeters consisting of liquid solutions, solid films, ceramics,crystalline materials, plastics, etc., are subject to imprecision andsystematic error due to environmental effects during field use, production,irradiation, and readout. Therefore, if these factors are not sufficientlyknown and understood, absorbed dose interpretations using such systems havereproducibility and accuracy values that are difficult to establish.Although, as indicated above, NBS in its high-dose calibrations (e.g.
schedule 49010S) administers to within prescribed uncertainty limitsstandard absorbed doses of gamma radiation under controlled environmentalconditions, the routine dosimeters for field use are subject to unevenquality control of manufacture and are occasionally susceptible to
anomalous batch-to-batch or intrabatch sensitivity differences, poorreproducibility of readout results, and adverse environmental effects.
In the case of absorbed dose evaluation based on mailed transfer NBS-controlled radiochromic film dosimeters (nominal dose range 1 x 10 3 to
5 x 10 4 Gy) that are traceable to 60 Co gamma-ray calibrations at NBS, the
uncertainty values cited above (± 5.2%) may be assumed as long as suitablecare against environmental and other sources of systematic error is
exercised.
A detailed list of the various sources of uncertainty that make up the
overall uncertainties given above may be obtained by requesting such
information from NBS
.
Appendix A
A-3
UNITED STATES DEPARTMENT OF COMMERCENational Bureau of StandardsGaithersburg. Maryland 2QB99
June 27, 1986
FEDERAL EXPRESS PRIORITY 1
Mr. John DoeSenior EngineerGamma Radiations, Inc.
123 University AvenueChicago, IL 60606
Dear Mr. Doe:
Reference: Your P.O. No. 12345
Enclosed are the packaged dosimeters which you requested for irradiation in
your facility. There are fourteen packages: thirteen for irradiation plus
one control package which should not be irradiated. Please do not open the
packages at any time; they provide a controlled environment for the dosi-meters. If the temperature of the packaged dosimeters is expected to
increase more than 10°C above room temperature during irradiation, pleaseprovide information on the temperature as a function of time for the longestirradiation period. Other irradiation data, such as date and time of irra-
diation, length of the irradiation period, and any other pertinent informationshould be included with the returned dosimeters. The nominal absorbed doses
received by these dosimeters should be within the range of 1 kGy (0.1 Mrad)
and 30 kGy (3.0 Mrad). Please return the dosimeters to us as soon as the
irradiations are completed so that we may get the results back to you promptly.
If you have any questions, please call me or Jim Humphreys at (301)921-2201.
Dene G. HockenCalibrations TechnicianX-Ray Physics GroupCenter for Radiation Research
Enclosures
Sincerely,
APPENDIX B
B-l
U.S. DEPARTMENT OF COMMERCENATIONAL BURCAU Of STANDARD!
QAITHERSBURQ. MARYLAND 20SSS
REPORT OF CALIBRATIONof
Gammacell 220 Irradiator
for
Gammaray, Inc.
999 Cobalt StreetMiami, FL 32111
Attention: James Doe
Ref. P.O. No.: 32123
Transfer dosimetry packets, consisting of five calibrated FWT-60-00 radlochromicdosimeters (NBS Batch 144), held between 5.0-mm thick blocks of polystyrene and
sealed Inside two thin polyethylene pouches (R.H. 43% at time of sealing), weresupplied to Gammaray for Irradiation in their Gammacell 220 irradiator facility.Upon their return to NBS,. the dosimeters were analyzed on 9 September 1985, at two
wavelengths (605 nm and 510 nm) using a Cary Model 219 spectrophotometer (3.5 nmS.B.W.). Absorbed dose Interpretations were made from a calibration of this batchof radlochromic dosimeters performed 1n April 1985. The results are summarized 1n
the following table:
NBS AbsorbedDosimeter Dose 1n H
2 0. kGy*No. (605 nm)
696-700 (Controls) 0
701-705 18.55706-710 9.00711-715 16.25716-720 U.40721-725 19.70726-730 18.90731-735 7.50736-740 23.20741-745 18.30746-750 19.60
Test 536/222222-86NBS DB 100/001XRG-321October 10, 198b
*1 kGy - 0.1 Mrad APPENDIX C
C-l
Test. 536/222222-86
NBS DB 100/001
XRG-321October 10, 1985Page 2 of 5 pages
The dosimeters were read 1n terms of optical absorbance before (A0 ) and after (A*)
Irradiation, using a Cary Model 219 spectrophotometer (3.5 nm S.B.W.), at two
optical wavelength settings/ 605 nm and 510 nm. Dosimeter film thicknesses wereread using a Mltutoyo Model DGS-E thickness gage. Values of Increase 1n opticalabsorbance per unit thickness (AA/mm, where aA Aj - A
Q ) are also Included.
Date,
Dosimeter TimeNo. ;
(605 nm) (510 nmof A
1
) Reading (605 nm)4(510 nm)
Thickness(mm)
AA/mm(605 nm)(510 nm
O 1S16v . 1J1U 0 0591 9/9/85 0.1516 0.0591 0.050fiQ7 n i R7n 0 0787 11*15 0 1563 0.0781vi v/ Ul 0 050
0 id?7 O 0597 M0 1435 0 0596 0 049 —Controls--
699 0.1496 0.0605N 0.1487 0.0599 0.051
700 0.1504 0.0599M 0.1507 0.0604 0.051
7m U. iHtJ 0 0591 9/9/85 1 4947 0 2256 0 050 27.04 3.3307n? U. I3UU n ofioi 1 1 • ?S11 iL J 1 (i?371 t JLJ( 0 0^0 27.47 3.3607m n i tqq M 0 ??dfi O OR1 26.07 3.16770d O OfiO"?
II1 635? 0 2380 0 053 28.01 3.353
705 0.1514 0.0627N
1.6253 0.2392 0.052 28.34 3.394
706 0.1498 0.0600 9/9/85 0.8804 0.1483 0.051 14.33 1.731
707 0.1526 0.0712 14:35 0.8906 0.1587 0.052 14.19 1.683708 0.1472 0.0598
N 0.8893 0.1476 0.050 14.84 1.756709 0.1551 0.0628
N0.9297 0.1537 0.051 15.19 1.782
710 0.1487 0.0638M
0.9136 0.1549 0.051 15.00 1.786
711 0.1625 0.0800 9/9/85 1.4276 0.2314 0.052 24.33 2.912712 0.1650 0.0742 14:45 1.4719 0.2291 0.053 24.66 2.923713 0.1563 0.0722
N1.3659 0.2209 0.052 23.26 2.860
714 0.1489 0.0598N
1.4138 0.2149 0.051 24.80 3.041715 0.1555 0.0604
N1.4299 0.2168 0.052 24.51 3.008
716 0.1547 0.0640 9/9/85 1.0597 0.1742 0.052 17.40 2.119717 0.1419 0.0586 15:00 1.0341 0.1673 0.051 17.49 2.131718 0.1494 0.0600
N1.0486 0.1675 0.050 17.98 2.150
719 0.1570 0.0646N
1.0935 0.1753 0.051 18.36 2.171720 0.1550 0.0643
N1.0759 0.1732 0.050 18.42 2.178
APPENDIX C
C-2
Test 536/222222-86NBS DB 100/001
XRG- 321
October 10, 1985Page 3 of 5 pages
Date,
Dosimeter Time
No. Aq of Aj Aj Thickness aA/mm
(605 nm)(510 nmj Reading (605 nm)(510 nmj (mm) (605 nm)(510 nm)
t CI U. 10** 3 n 07fift 7/7/ OJ 1 6103 0 ?5?*i 0 05? ?7 ROC 1 .ou 3 37QJ. J / 7
7771 CC U. 10c7 n 07R7 15*10 1 5869A • JOU7 0 ?474V • C*t # *t 0 0^0 ?ft 4ftCO • HO 3 374J. J / H
723 0.1506 0.0599 1.6251 0.2367 0.051 28.91 3.467724 0.1449 0.0596
«1.6124 0.2376 0.050 29.35 3.560
/ n irmv. 1901 0 0603 N1 6466 0 2411 0 051 ?Q ?4C7 . c*t 3 >t4HJ. Of 0
7?fi/ CO U. lOOU 0 0640 9/9/857/ 7/ W«J 1.5462 0 2343 0 05? 26 73 3 ?7*iO.C/ J
7?71 CI U. 134
1
0 0660 15*15 1.5674 0 2401 0 OH? ?7 ?? 3 34ft
728 0.1456 0.0628M
1.5400 0.2312 0.050 27.89 3.368729 0.1487 0.0619
N1.6037 0.2309 0.051 28.53 3.314
730 U. 1HOO O 0613 M1 5786 0 2339 0 0«il ?R 10CO. 1U 3 3ft4J . JOH
731 n 1H31U. 10Jl 0 0603 9/9/857/ 7/ O.J 0 7674 0 1338 o om 1? 04AC .U*T 1 441A • **? 1
73?1 Jc U. 1 OJO O 0fi?7 15*?0 0 8066 0 140 1* 0 0*>? 1? *»fiAC . OO 1 4Qfi
733 0.1467 0.0622M
0.7493 0.1348 0.050 12.05 1.452734 0.1533 0.0626
M 0.7802 0.1384 0.051 12.29 1.48673R/ JO U. locO U.UOU/
M 0 7fiQ0V/ . / U7U 0 1 344U . A Oft o n^n 1 9 371c • J J 1 A7AA . *T / H
73fi/ JO U. lolc o ofi?o Q/q/pr;7/ 7/ OJ 1 8718A .0 1 AO 0 ?74ft o nmU .UOl 33 7AJJ. /H a i it.*• 1/
J
737/J/ n i qi aU. 1 010 n 07?ftU.U/ CO AO • JU 1 74HQA . / H07 U • COOO U.UOl 31 39Jl • Jc 3 RA.7J.Of J
73ft/ JO n 1 A77U. / A .OUO/ 0 ?fi3*»UiLOJO o n<>iU.UOl 33 AO.JJ .07 * .uuo
739 0.1508 0.0671M
1.8354 0.2701 0.050 33.69 4.060740 0.1469 0.0599
it
1.7632 0.2608 O.049 32.99 4.100
741 0.1614 0.0790 9/9/85 1.4965 0.2416 0.052 25.68 3.127742 0.1516 0.0666 15:40 1.5044 0.2305 0.052 26.02 3.152743 0.1581 0.0620
M1.5585 0.2317 0.051 27.46 3.327
744 0.1471 0.0608It
1.5296 0.2278 0.050 27.65 3.340745 0.1464 0.0602
n1.5344 0.2273 0.051 27.22 3.276
746 0.1501 0.0629 9/9/85 1.6048 0.2418 0.051 28.52 3.508747 0.1518 0.0604 15:45 1.6099 0.2355 0.050 29.16 3.502748 0.1538 0.0644
M1.6830 0.2481 0.052 29.41 3.533
749 0.1488 0.0680tt
1.5938 0.2435 0.052 27.79 3.375750 0.1467 0.0642
M1.6026 0.2380 0.051 28.55 3.408
APPENDIX C
C-3
Test 536/222222-86NBS DB 100/001XR6- 321October 10, 1985Page 4 of 5 pages
Analysis of the dosimeter response consists of determining the mean aA/mm for eachgroup of five dosimeters irradiated together and the standard deviation of eachgroup as shown below.
Dosimeter Mean AA/mm X Std. Dev., a ,n-i
No. (605 nm) (510 nm) (605 nm) (510 nm)
696-700 —Controls—
701-705 27.39 3.321 3.24X 2.70X
706-710 14.71 1.748 2.94X 2.42X
711-715 24.31 2.949 2.52X 2.51X
716-720 17.93 2.150 2.65X 1.17%
721-725 28.76 3.465 2.20X 2.54X
726-730 27.69 3.338 2.59X 1.31%
731-735 12.25 1.470 1.73X 1.56X
736-740 33.09 4.036 3.13X 3.07X
741-745 26.81 3.244 3.33X 3.05X
746-750 28.69 3.465 2.20X 2.00X
APPENDIX C
C-4
Test 536/222222-86
NBS DB 100/001
XRG- 321
October 10, 1985Page 5 of 5 pages
The attached page describes uncertainties and related factors In high-dosecalibrations, such as the one covered by this Report of Calibration. Any questionsregarding environmental conditions, different types- of materials used, andsystematic uncertainties associated with these calibrations can be answered by thisattachment. If there are further questions, they should be directed to the firstIndividual named below.
Measurements were made by
D. G. Hocken, Calibrations Technician(30i)921-2201
Approved by
J. W. Motz, LeaderX-Ray Physics Group
For the 01 rector
R. S. Caswell, ChiefIonizing Radiation DivisionCenter for Radiation Research
APPENDIX C
C-5
UNCERTAINTIES AND RELATED FACTORS IN HIGH-DOSE CALIBRATIONS
Standard High-Dose Gamma-Ray Irradiations at NBS(Estimated uncertainty: ± 3.3% at a 99% confidence level)
The high-dose calibrations at NBS (schedule 49010S) involve the administrationof 60 Co gamma radiation absorbed doses in certain materials (e.g., water,carbon, aluminum, silicon, polystyrene, etc.), under environmentally controlledconditions. The dose values are based on standard graphite calorimetrymeasurements, which are corrected by certain modifying factors (the estimatedphoton spectrum, tabulated weighing factors, such as radiation energyabsorption and attenuation factors, and source decay factors). Theirradiations are usually carried out using the NBS 60 Co gamma-ray pool source.The uncertainty values cited above are for the absorbed doses given typicalthin dosimeters (5 or less irradiated at a time) held under layersapproximating electron equilibrium in a given material, in the absorbed doseregion of 1 KGy and upward.
Absorbed Dose Evaluations Based on Traceability throughMailed Chemical Transfer Dosimeters(Estimated uncertainty: ± 5.2% at a 99% confidence level)
It must be recognized by calibration users that routinely applied chemicaldosimeters consisting of liquid solutions, solid films, ceramics, crystallinematerials, plastics, etc., are subject to imprecision and systematic error due
to environmental effects during field use, production, irradiation, andreadout. Therefore, if these factors are not sufficiently known andunderstood, absorbed dose interpretations using such systems havereproducibility and accuracy values that are difficult to establish. Although,as indicated above, NBS in its high-dose calibrations (e.g. schedule 49010S)administers to within prescribed uncertainty limits standard absorbed doses of
gamma radiation under controlled environmental conditions, the routinedosimeters for field use are subject to uneven quality control of manufactureand are occasionally susceptible to anomalous batch-to-batch or intrabatchsensitivity differences, poor reproducibility of readout results, and adverse
environmental effects.
In the case of absorbed dose evaluation based on mailed transfer NBS-
controlled radiochromic film dosimeters (nominal dose range 1 x 10 3 to 5 x 10 A
Gy) that are traceable to 60 Co gamma-ray calibrations at NBS, the uncertainty
values cited above (± 5.2%) may be assumed as long as suitable care against
environmental and other sources of systematic error is exercised.
A detailed list of the various sources of uncertainty that make up the overall
uncertainties given above may be obtained by requesting such information from
NBS.
Appendix C
C-6
NBS-114A (REV. 2-80)
U.S. DEPT. OF COMM.
BIBLIOGRAPHIC DATASHEET (See instructions)
1. PUBLICATION ORREPORT NO.
NBS/SP-250/11
2. Performing Organ. Report No. 3. Publication Date
March 1988
4. TITLE AND SUBTITLE
NBS Measurement Services:
National Bureau of Standards High Dose Calibration Services
5. AUTHOR(S)
J.C. Humphreys, Dene Hocken, and William L. McLaughlin6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)
NATIONAL BUREAU OF STANDARDSU.S. DEPARTMENT OF COMMERCEGAITHERSBURG, MD 20899
7. Contract/Grant No.
8. Type of Report & Period Covered
Final
9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)
Same as item 6
.
10. SUPPLEMENTARY NOTES
Library of Congrss Catalog Card Number 88-600506
| |Document describes a computer program; SF-185, FIPS Software Summary, is attached.
11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a si gnificantbibliography or literature survey, mention it here)
This document describes calibration services available at the National Bureau ofStandards for the standardization of high absorbed dose measurements of ionizingradiation. The areas of application of such measurements include medical productsterilization, electronic device radiation hardness testing and food processing.Detailed descriptions of the NBS dosimetry procedures and uncertainty assessmentsare given. Measurement assurance program techniques are discussed.
12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by s-emicolon s)
dosimeter calibration; ionizing radiation; irradiation facilities;
measurement assurance program; uncertainties
13. AVAILABILITY
Unlimited
| |For Official Distribution. Do Not 'Release to NTiS
{q3 Order From Superintendent of Documents, U.S. Government (Printing Off ice, Washington, D.C.20402.
Qjj Order From National Technical limffonnation Service (iNTIS), Springfield, VA. 22161
14. NO. OFPRINTED PAGES
49
15. Price
tf-U.S. Government Printing Office : 1988 - 201-597/82534
USCOMM-DC 4M3-P80
THE SP 250 SERIES ON NBS MEASUREMENT SERVICES*
SP 250-1 Spectral Radiance Calibrations
003-003-02792 $3.50
SP 250-2 Far Ultraviolet Detector Standards
003-003-02810-0 $4.25
SP 250-3 Radiometric Standards In the Vacuum
Ultraviolet
003-003-02806-1 $6.50
SP 250-4 Frlcke Dosimetry in High-Energy Electron Beams
003-003-0281 6-9 $2.75
SP 250-5 Alpha-Particle Calibrations
SN003-003-0283-1 $2.00
SP 250-6 Regular Spectral Transmlttance
003-003-02805-3 $3.25
SP 250-7 Radiance Temperature Calibrations
003-O03-O2827-4 $2.25
SP 250-8 Spectral Reflectance
003-003-02812-6 $7.00
SP 250-9 Calibration of Beta-Particle-Emlttlng
Ophthalmic Applicators
003-003-02817-7 $2.00
SP 250-10 Radioactivity Calibrations with the "4ir"
Gamma Ionization Chamber, and Other
Radioactivity Calibration Capabilities
003-003-02824-0 $2.25
SP 250-1 1 Dosimetry for High-Dose Applications
SP 250-12 Neutron Personnel Dosimetry
003-003-O2811-8 $2.50
SP 250-13 Activation Foil irradiation with Californium
Fission Sources
SP 250-14 Activation Foil Irradiation by Reactor Cavity
Fission Sources
SP 250-15 Photometric Calibrations
SN003-003-02835-5 $4.25
SP 250-16 Calibration of X-Ray and Gamma-Ray
Measuring Instruments
SP 250-17 The NBS Photodetector Spectral Response
Calibration Transfer Program
SP 250-18 Neutron Source Strength Calibrations
SP 250-19 Calibration of Gamma-Ray-Emitting
Brachytherapy Sources
SP 250-20 Spectral Irradlance Calibrations
003-003-02829-1 $5.50
SP 250-21 Calibration of Beta-Particle
Radiation Instrumentation
SP 250-22 Platinum Resistance Thermometer
Calibrations
003-003-02831-2 $17.00
SP 250-23 Uquld-ln-Glass Thermometer
Calibration Service
SP 250-24 Standard Cell Calibrations
003-003-02825-8 $2.75
SP 250-25 Calibration Service for Inductive
Voltage Dividers
SP 250-26 Phase Angle Calibrations
SP 250-27 AC-DC Difference Calibrations
SP 250-28 Solid-State DC Voltage Standard Calibrations
SN003--003-02842-8 $2.00
SP 250-29 Traceable Frequency Calibrations
SN003-003-02844-4 $2.25
SP 250-30 GOES Satellite Time Code Dissemination:
Description and Operation
SN003-003-02845-2 $2.75
* Those entries containing a stock number (003-003—) and price can be purchased from the Superintendent of Documents, U.S.
Government Printing Office, Washington, DC 20402. GPO will accept checks, money orders, VISA, and Mastercharge. For more informa-
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